Spring remedial treatments to improve canopy structure and yield in winter oilseed rape


Cereals & Oilseeds
Project code:
01 January 1999 - 30 June 2002
AHDB Cereals & Oilseeds.
AHDB sector cost:
£183,308 from HGCA (project no. 2097).
Project leader:
G D LUNN, Division of Agricultural Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, LE12 5RD. J H SPINK, A WADE & R W CLARE, ADAS Rosemaund, Preston Wynne, Herefordshire, HR1 3PG



About this project


Previous research, funded by HGCA and Defra, has shown that oilseed rape green canopies can be too large, leading to poor utilisation of light and reduced yields.  This may be due to early establishment, plentiful nitrogen availability and mild winter conditions.   

This project aimed to identify crops requiring remediation to attain optimum size during pod filling and the most effective methods of achieving it. The triazole fungicides tebuconazole (Folicur) and metconazole (Caramba) have plant-growth-regulating activity due to their inhibition of gibberellin synthesis. Another previously investigated technique is mowing the crop in late winter. 

A series of experiments investigated optimum timing of the PGR chemicals, and use of mowing, in relation to canopy size and variety of oilseed rape. Crops of the conventional variety Apex and the hybrid Pronto were grown at ADAS Rosemaund and ADAS High Mowthorpe in 1999, 2000 and 2001.  

In 1999, the effect of timing (March-May), dose and mixture of the PGR chemicals with chlormequat on growth and yield was studied. The chemicals significantly reduced crop height and lodging when applied at stem extension (GS 2) in March. Later applications (up to early May) at green bud - early flowering (GS 3 - 5) increased yield by up to 0.6 t ha-1.   

Subsequent trials in 2000 and 2001 compared the effect of early (March, greatest height and lodging effects previously) and late applications (potentially more beneficial for yield) on crops of different canopy sizes. A range of canopy sizes resulted from the two sowing dates (early September/early October) and two seed rates (120 and 60 seeds m-2).

At both sites, yield improvements were produced most consistently from spraying the largest crops (early-sown, high seed rates) with PGRs, with GAIs > 0.5-1 in March or 1.5-2 in April. Spraying small crops could result in small yield losses.  Benefits were possible from both March and April full rate sprays, but the April sprays were generally more consistent and gave greater yield benefits (up to 1 t ha-1). Yield enhancements greater than about 0.2 t ha-1 were needed for an economic return.  

Growth analysis data was used to derive a relationship between crop fresh weight  (FW) and green area index (GAI = 0.8*(FW in kg)), which can be used to identify the crops most suitable for remediation. Yield benefits were generally due to increased numbers of seeds per square metre and increased thousand seed weight. This could be due to enhanced assimilate supply and seed survival, better light interception and partitioning and better combine harvest seed recovery. 

Mowing was attempted in all years but was not possible in 1999 and 2001 due to soil conditions. In 2000 mowing generally caused small yield decreases, since the canopies being mown were not excessive to start with.